Preliminary Report 
Eastern Area Cruise Number 40 
Coronado Islands 
Itinerary: 
1040 - 1 May 1968 Land on North Island, Coronados Islands. 
1400 -1530 - 1 May 1968 Survey Center Island from raft. 
0800 - 2 May 1968 Depart North Island. 
During the period 1-2 May 1968 Robert DeLong and Richard Crossin 
surveyed North Island in the Coronados Islands offshore Baja California, 
Mexico. A brief run with a raft was made about the two islets compris¬ 
ing Center Island,but no landing was made. The following day we were 
transported to the islands and picked up by the charter vessel SIOUX CITY. 
The west and south sides of North Island were surveyed by raft, and seals 
and sea birds were recorded. All other pertinent data are included in 
the accounts below. Unless otherwise stated, all discussion concerns 
data collected on North Island. 
SPECIES ACCOUNTS 
Oceanodroma melania Black Petrel 
An unsuccessful preliminary search was made during daylight hours 
for this species. After observing the nestsites at night, it is doubt¬ 
ful if we would have detected the birds during the daytime if they had 
been there. Exactly at full dark,birds began flying in over the island 
and calls would soon be heard from all directions. The appearance of 
the storm petrels was exactly coincident with termination of Western 
Gull movements. This flight timing of the storm petrels has likely 
evolved in direct response to the movements of the predatory gulls. 
In the Central Pacific the White-throated Storm Petrel (Nesofregetta 
albigularis ), with no resident predators, begins flying over the nest¬ 
ing islands in early evening, long before full dark. Flight activity 
in the Black Petrel was most intense during the first few hours after 
dark and essentially stopped by 2400 hours. DeLong noted an increase 
in flying birds near the water’s edge at about 0100, perhaps of birds 
departing the island. 
Two characteristic calls are given by the birds. One is rather 
musical and given primarily in flight as the birds presumably trace 
back and forth over the nestsites. Occasionally this call may be 
uttered by a bird within the nest cavity. The other call, which is 
a variable "twitter", is apparently only given from the nest chamber. 
This latter call may be continuous for many minutes. Tape recordings 
of both calls were made. 
